Mexico has been able to "adopt practices that allow them to compete on quality and come in at a lower in price than what most California growers can do," points out Sumner.

For several years, many supermarkets have launched marketing efforts to highlight California-grown produce.

While food shoppers may like the sound of that, it's not clear they're willing to pay very much for it.

He points to the textile industry for a comparison.

"We could imagine paying seventy-five dollars for a shirt or a blouse because we want textile workers to make twenty-five dollars an hour," Sumner points out.

But textile workers don't earn those kinds of wages at this time. And most manufactured textile products Americans use come in from elsewhere in the world.

When it comes to California produce, Sumner says consumers will decide with their wallets what farm labor wages they're willing to support.

In surveying five grocery stores near downtown Sacramento, this reporter found asparagus prices that ranged from $2.99 - $6.99 a pound. Some labels read "product of the U.S.A." but did not specify if the asparagus was grown in California.

Spears grown in Mexico had the lowest price tag. For double that price you can buy asparagus harvested in the Capay Valley, fifty miles from Sacramento.